Servo Motor Example VI?

[TJones]

Hi there,

I am using a cRIO with 9425, 9476, 9401, and 9263 modules. I am in need of controlling a stepper motor using existing ramp up and ramp down VI's (that I already have) to control the speed. I was wondering if there were any generic stepper motor VI's that I could use with my cRIO. I am concerned with speed, position, direction, and the ability to use full step mode or half step mode.

I have encountered this fairly helpful educational example: http://etidweb.tamu.edu/projects/labview/stepper/vi.htm. I am having trouble deciphering some of the modules used in the example, however, and could use some help translating from their version (LabView 5.0) to mine (LabView 8.2). For example - they appear to be using some sort of "Dig Port" subVI that I'm unfamiliar with. What should I use to interface with my cRIO?

If stated example doesn't appear valid for my application, any other examples of stepper control you can provide would be of tremendous help.


Thank you!

Trevor Jones

[TJones]

Anyone have any ideas for this? Or do you know of an existing thread that might have a helpful stepper motor VI example?

[BullDozier]

I have taken a look at that link at your link and found that it will be complicated to use this as a basis for cRIO development.  The cRIO development relies on FPGA code along with Real Time code.  The example was written using our Traditional DAQ functions.  Now we use DAQmx which is just a newer DAQ protocol that is easier to understand and learn.  To learn more about compact RIO and how you implement code on a cRIO, you can visit that site on our webpage at www.ni.com/compactrio/.

Typically steppers are controlled with NI-Motion VI's as well as NI's motion boards. Since all of the cards you mentioned are Digital or Analog I/O cards, It will be complicated to design a system to perform the same tasks our motion boards perform right out of the box.  It is possible, but you will need to add a stepper drive into this equation because the digital cards will probably not have the strength to drive the cards on their own.

To keep up with position, speed, velocity, and step mode, you will have to custom write VI's that will work with your cRIO modules.  What ramp up and ramp down VI's do you already have?  These may suffice for what you need to do if they were written for the FPGA+RT architecture of the cRIO environment. 

Let me know if I can help with anything else!

Evan Dozier

[Jochen]

Trevor,

Evan is correct that it might be a quite complex task to create a complete motion control application from the scratch on a cRIO platform. To make this task much easier, NI provides the NI SoftMotion Development Module. This is a powerful tool that provides high-level functions similar to the NI-Motion API. On the controller level there is a ready to run trajectory generator, a spline engine and powerful control algorithms. The latest version comes also with stepper motor support. You will also find ready to run examples for implementing motion control applications on a cRIO platrom with this module.

I hope this helps,

Jochen Klier
National Instruments